- Jesse Eisenberg as Mark Zuckerberg[11]
- Andrew Garfield as Eduardo Saverin[12]
- Justin Timberlake as Sean Parker[13]
- Armie Hammer as Cameron and Tyler Winklevoss[14]
- Max Minghella as Divya Narendra[14]
- Brenda Song as Christy Lee[14]
- Rashida Jones as Marylin Delpy[15][16]
- John Getz as Sy[17]
- David Selby as Gage[17]
- Denise Grayson as Gretchen[17]
- Douglas Urbanski as Larry Summers[17]
- Rooney Mara as Erica Albright[14]
- Joseph Mazzello as Dustin Moskovitz[14]
- Dustin Fitzsimons as The Phoenix – S K Club President[18]
- Wallace Langham as Peter Thiel[19]
- Patrick Mapel as Chris Hughes[14]
- Dakota Johnson as Amelia Ritter[14]
- Malese Jow as Alice Cantwel[20]
- Trevor Wright as B.U. Guy in Bra[17]
- Shelby Young as K.C.[21]
- Aaron Sorkin as Ad Executive[17]
- Steve Sires as Bill Gates[22]
- Caleb Landry Jones as a fraternity brother[23]
Josh Pence is the body double for Hammer, whose likeness was digitally imposed onto Pence's body. He is listed in the end credits as playing Tyler Winklevoss alongside Hammer, though he also shot scenes as Cameron. He also appears in a cameo role as the man being detoured from the bathroom by Zuckerberg and Saverin.[24]
